neutralize?

[drj]

My boss wants to feed twelve 30A, 3phase 480v trailers from a service that offers 120/240 service with a step up 112.5KVa transformer that has a 208V primary delta with a 480Y/277 volt secondary.

The loads will not be uniform, nor constant.

No neutral will be hooked up??

What will this do to the transformer.

Is this safe?

Thanks

 

[iwire]

My boss wants to feed twelve 30A, 3phase 480v trailers from a service that offers 120/240 service with a step up 112.5KVa transformer that has a 208V primary delta with a 480Y/277 volt secondary.

What is the actual load of a '30A trailer'?

The loads will not be uniform, nor constant.

Can you explain that a bit more?

No neutral will be hooked up??

What will this do to the transformer.

Is this safe?

Without knowing the actual load each trailer draws it is tough to answer.

As far as the neutral, if you don't need it you don't have to use it but you do have to bond XO to the EGC and the earth.

 

[infinity]

I agree with Bob, without knowing the actual loads it tough to say if the transformer is large enough. Since the load is 3 phase, 480 no neutral is required. This is what I came up for a maximum secondary transformer load:

(112.5*1000)/(480*1.73)= 135.5 amps

 

[jim dungar]

My boss wants to feed twelve 30A, 3phase 480v trailers from a service that offers 120/240 service with a step up 112.5KVa transformer that has a 208V primary delta with a 480Y/277 volt secondary.

The loads will not be uniform, nor constant.

No neutral will be hooked up??

What will this do to the transformer.

Is this safe?

Thanks

Do I have this correct?
Your service is 240/120 3Phase 4Wire but your transformers are 208V 3-phase on the low voltage windings.

If you apply 240V to a 208V transformer you will get more than 480V out. Does your transformer have enough taps to accommodate this high (10%) of an incoming voltage?

 

[dbuckley]

Think there is a typo here:

My boss wants to feed twelve 30A, 3phase 480v trailers from a service that offers 120/240 service with a step up 112.5KVa transformer that has a 208V primary delta with a 480Y/277 volt secondary.

You can't have a three phase 120/240 supply, so I think you mean a normal 208/120 three phase supply.

In terms of an arrangement, a delta primary on three wire 208V with a wye secondary producing four wire 480/277 is perfectly acceptable, though a little unusual. The supply from the secondary is just an ordinary SDS, so normal SDS arrangements apply.

In terms of an unbalanced load, your PoCO will expect you to have your load balanced-ish. If your load is overall balanced-ish then my sums tells me the transformer is of about adequate capacity, assuming it really can deliver 112.5KVa continuously.

 

[chris kennedy]

You can't have a three phase 120/240 supply

120/240 3? 4Wire (Delta High Leg)

 

[iwire]

http://www.electrical-contractor.net/forums/ubbthreads.php?ubb=cfrm

 

[drj]

Thanks everyone!

Thanks everyone!

I was surprised to get such quick, knowledgeable and informative responses. I suppose there was no way for me to hide the fact that experienced electricians were not in charge of this job (You Tube reference).

The transformer is hooked up, not to code, but its hooked up. I'll let you know load values or if anything interesting happens.

Have a great holiday season